Most manufacturers of dryer drums and steam fittings for dryer drums have their own systems for mounting the steam and condensation removal passages to and from the dryer through at least one of the mounting journals.
In a simple system the steam inlet passages is through one of the journals and the condensate removal passage passes throgh the other journal, i.e. on opposite ends of the dryer drum. It is also known to concentrically provide an air space, steam inlet tube and condensate return pipe within a single journal of the dryer drum.
It will be apparent that the steam tube and condensate return pipe rotate with the dryer drum and thus a suitable rotary coupling must be provided to connect these tubes or pipes to corresponding fixed conduits. Generally, such couplings are connected by fittings bolted directly to the outer end of the dryer journal. When concentric steam and condensate passages are used the fittings are fixed to the journal and in some manner sealed to the tube for steam passage through the journal into the dryer drum (the condensate pipe passes directly to the rotary coupling with no intermediate fitting or nipple). Such sealed connections between the fittings and steam tube are in many cases formed within the confines of the hollow journal itself.
It is common practice to maintain an air space between the inner wall of the journal, i.e. of the hollow journal and the steam tube and/or condensate return pipe passing through the journal. These annular insulating chambers are sealed at the dryer end of the journal by a suitable flange generally bolted to the head of the dryer and at the opposite end by a suitable insert which forms a part of a fitting bolted to the free end of the journal and functioning to center the tube or pipe passing through the journal and connect, in sealed relation, this tube or pipe with a fitting or nipple leading to a rotary coupling. Such sealed air spaces are intended to insulate the dryer journal from the hot steam and condensate passing therethrough, however, while a dead air space provides a good insulator the sealed space results in building up the air pressure by heating of the trapped air which reduced the effectiveness of the air space for impairing heat transfer from the tube to the journal.